A typical alternating-current surface discharge type panel used as a plasma display panel (hereinafter referred to as “panel”) has many discharge cells between a front plate and a back plate that are faced to each other.
The front plate has the following elements:                a plurality of display electrode pairs disposed in parallel on a front glass substrate; and        a dielectric layer and a protective layer for covering the display electrode pairs.Here, each display electrode pair is formed of a pair of scan electrode and sustain electrode. The back plate has the following elements:        a plurality of data electrodes disposed in parallel on a back glass substrate;        a dielectric layer for covering the data electrodes;        a plurality of barrier ribs disposed on the dielectric layer in parallel with the data electrodes; and        phosphor layers disposed on the surface of the dielectric layer and on side surfaces of the barrier ribs.        
The front plate and back plate are faced to each other so that the display electrode pairs and the data electrodes three-dimensionally intersect, and are sealed. Discharge gas containing xenon with a partial pressure of 5%, for example, is filled into a discharge space in the sealed product. Discharge cells are disposed in intersecting parts of the display electrode pairs and the data electrodes. In the panel having this structure, ultraviolet rays are emitted by gas discharge in each discharge cell. The ultraviolet rays excite respective phosphors of red (R), green (G), and blue (B) to emit light, and thus provide color display.
A subfield method is generally used as a method of driving the panel. In this method, one field time period is divided into a plurality of subfields (hereinafter referred to as “SF”), and the subfields at which light is emitted are combined, thereby performing gradation display.
Each subfield has an initializing period, an addressing period, and a sustaining period. In the initializing period, initializing discharge is performed to form a wall charge required for a subsequent writing operation on each electrode. The initializing operation includes an initializing operation (hereinafter referred to as “all-cell initializing operation”) of causing initializing discharge in all discharge cells, and an initializing operation (hereinafter referred to as “selection initializing operation”) of causing initializing discharge in a discharge cell having performed sustaining discharge.
In the writing time period, writing discharge is selectively caused to form a wall charge in a discharge cell where display is to be performed. In the sustaining period, sustain pulses are alternately applied to the display electrode pairs formed of the scan electrodes and the sustain electrodes, sustaining discharge is caused in the discharge cell having performed writing discharge, and a phosphor layer of the corresponding discharge cell is light-emitted, thereby displaying an image.
Of the subfield method, a new driving method is disclosed. In this driving method, the initializing discharge is performed using a gently varying voltage waveform, and the initializing discharge is selectively applied to the discharge cell having performed sustaining discharge. Thus, light emission that is not related to the gradation display is minimized, and the contrast ratio is improved.
Specifically, in the initializing period of one of a plurality of subfields, for example, the all-cell initializing operation of causing discharge from all discharge cells is performed. In the initializing period of the other subfield, the selection initializing operation of initializing only the discharge cell having performed sustaining discharge is performed. As a result, light emission that is not related to the display is only the light emission accompanying the discharge of the all-cell initializing operation, and an image having sharp contrast can be displayed (e.g. patent document 1).
This driving manner allows image display of sharp contrast, because the luminance (hereinafter referred to as “black luminance”) in a black display region during the light emission that is not related to the image display, namely during non-display of video, is only due to weak light emission in the all-cell initializing operation.
The number of discharge cells has been increased in response to the improvement of the definition of the panels and the enlargement of the screen, and the number of subfields is increased for improving the false outline of moving pictures and the image display quality, so that the speed-up of the writing operation is further demanded.
The all-cell initializing operation of initializing all discharge cells also forms wall charge required for the writing operation as discussed above, reduces the discharge delay, and generates priming in order to stably cause writing discharge. Therefore, for speeding up the writing operation, a method of increasing the priming is effective. When the number of subfields (hereinafter referred to as “the number of all-cell initializations”) where the all-cell initializing operation is performed in one field time period is increased, however, the black luminance increases to degrade the contrast and image display quality.
Therefore, another panel driving method is proposed (e.g. patent document 2). In this method, the initializing operation in the initializing period of each subfield is determined to be the all-cell initializing operation or the selection initializing operation based on the Average Picture Level (APL) of an image signal to be displayed, thereby increasing or decreasing the number of all-cell initializations. This method allows stable and high-speed writing while suppressing the increase in black luminance.
However, the wall charge and priming generated by the all-cell initializing operation largely depend on the discharge characteristics such as discharge start voltage, and the discharge characteristics depend on the temperature of the panel. Even when the above-mentioned driving method is employed, the temperature range is disadvantageously restricted to some extent where driving of a panel allowing stable and high-speed writing while the increase in black luminance is suppressed can be performed. Additionally, the discharge characteristics of the panel depend on power-on accumulated time, so that a plasma display device cannot be easily controlled on an optimal condition, from the initial stage of its use, and regardless of the power-on accumulated time.
[Patent document 1] Japanese Patent Unexamined Publication No. 2000-242224
[Patent document 2] Japanese Patent Unexamined Publication No. 2005-215132